1. Field of the Invention
The present invention relates to heavy duty pneumatic tires.
2. Description of the Related Art
A tread of a tire includes a tread surface. The tread surface can contact with a road surface. The tread is formed of a crosslinked rubber.
In a heavy duty pneumatic tire mounted to a truck, a bus, and the like, a plurality of grooves are typically formed, in a tread, so as to extend in the circumferential direction, so that a plurality of ribs are formed. Among these ribs, ribs formed in outermost portions in the axial direction are referred to as shoulder ribs, and there is a problem that uneven wear is likely to occur in the shoulder ribs. This tendency is significant particularly in a tire mounted to a steered wheel of a vehicle. Various measures for addressing the uneven wear of a tread are suggested. The exemplary measures are disclosed in U.S. Pat. No. 4,480,671, JP2003-341305, JP03-011921 (U.S. Pat. No. 4,480,671), JP2005-028947 (US2005/0006016), JP03-253408, and JP2006-527686 (US2006/0090826).
The thickness of the shoulder rib may be gradually reduced from the inner side toward the outer side in the axial direction due to wear. The wear that causes such a state is referred to as shoulder wear. In order to address the shoulder wear, a review has been made such that a shape in which a tire contacts with the ground is adjusted by adjustment of a length over which the shoulder rib contacts with the ground.
In a tread having shoulder ribs that contact with the ground over a great length, load is concentrated on end portions located in outermost portions of the shoulder ribs in the axial direction, and an abnormally high ground contact pressure may be applied to the end portions. When the shoulder ribs are released from the ground contacting state due to rotation of the tire, the end portions slide on a road surface. In this case, the ends of the shoulder ribs rub, so that a stepped portion may be formed in the end portion. The wear that causes generation of the stepped portion in the end portion of the shoulder rib is referred to as step wear.
Through the review of a shape in which a tire contacts with the ground, generation of the shoulder wear has been restrained. However, another problem of the step wear arises anew. Consequently, generation of uneven wear has not been sufficiently restrained.
An object of the present invention is to make available a heavy duty pneumatic tire that restrains generation of uneven wear.